Leave jewellery endlessly to mythical creature (6)
I believe the answer is:
goblin
'mythical creature' is the definition.
(I know that goblin is a type of mythical creature)
'leave jewellery endlessly' is the wordplay.
'leave' becomes 'go' (to go is to depart or leave).
'jewellery' becomes 'bling' (informal term for jewellery).
'endlessly' means to remove the last letter.
'bling' with its final letter removed is 'blin'.
'go'+'blin'='GOBLIN'
'to' acts as a link.
(Other definitions for goblin that I've seen before include "Mischievous sprite" , "Dwarf-like creature" , "Malevolent imp" , "mischievous spirit" , "Mischievous ugly creature of folklore" .)